The general principle of operation of cylinder locks is known. In these, the bolt is usually operated by a cylinder (or plug) rotated within a corresponding cylindrical seat provided in the lock body. The cylinder is rotated by a cut key previously inserted into it, and is made possible by correctly arranging a plurality of pins housed partly in radial seats provided in the plug and partly in the extension of said seats provided in the cylindrical cavity housing it. As each pin is divided into two parts, the plug can be rotated only if the separation surface between the two parts of each pin coincides with the surface of discontinuity between the plug and relative seat. This state is achieved by correct cutting of the key which is inserted into the plug, to release it before rotating it.
The degree of reliability of a lock of this type corresponds to the number of variable factors which participate in forming that "combination" which enables the lock to be operated, and in particular the cross-section of the key and of the corresponding insertion seat in the plug, the number of pins and the number of positions which each pin can assume.
The possibility of finding two different locks operable by the same key is currently very remote, and hence the degree of reliability of such security locks is fairly high. However a wrongdoer expert in security locks can insert special tools into the opening in the plug and position the various pins in the same manner in which they would be positioned by the corresponding cut key, to hence succeed in rotating the key.
In order to prevent this tampering a security lock has been proposed in which the plug can be rotated only if the various pins are correctly positioned both axially and rotationally, in such a manner as to deactivate a special rake element which in addition to the pins also prevents the plug rotating within its seat.
In this known type of lock, known as a MEDECO.TM. lock, the notches are cut in the key by a cutter which instead of being positioned only perpendicular to the key to be cut can also be positioned inclined by .+-.20.degree. to the horizontal, and hence able to form inclined notches in the key. If in addition that end of the pins in contact with the key is of dihedron shape, inserting the key into the plug results not only in axial displacement but also rotation of the pins, corresponding to the inclination of the notches present in said key.
In this manner the double result is obtained of increasing the number of variable parameters which define a lock, and of making it practically impossible to operate the pins from the outside, so substantially increasing the degree of reliability of the lock.
In order to define the cutting code for the key, there is associated with the code defining the axial position of each pin a letter which can either be C (in the case of a perpendicular cut--Central), or R (in the case of a cut rotated through 20.degree. clockwise--Right), or L (in the case of a cut rotated through 20.degree. anticlockwise--Left).
In order to still further increase the number of variable parameters in a MEDECO.TM. lock, it has been proposed to also vary the shape of the wedge-shaped end of each pin, in the sense that besides being of symmetrical dihedron shape it can also be of asymmetrical dihedron shape with the sharp edge either forward or rearward of its position on the pin axis. The three forward positions are conventionally indicated by a letter, namely K, B or Q, preceding the letter identifying the three corresponding centered positions by one place, whereas the three rearward positions are conventionally indicated by a letter, namely M, D or S, following the letter identifying the three centered positions by one place.
The aforedescribed MEDECO.TM. locks have a very high degree of reliability, however they suffer from a serious problem relating to code-cutting the relative key, ie cutting keys from the identifying code for each pin of the corresponding key. In this respect, each notch key has to be cut with a cutter which not only forms the notch in the key to the required depth but also takes account of the particular shape of the pin, ie it must be able to be positioned perpendicular to the key axis or rotated through 20.degree. or -20.degree. from it, and must also be able to be shifted axially along the key shank by an amount corresponding to the particular asymmetry of the tip of the pin.
Machines currently exist for code-cutting (ie without using a key to be duplicated but knowing only the cutting code), both for MEDECO.TM. keys with a symmetrical wedge pin and for MEDECO.TM. keys with an asymmetrical wedge pin, but there are no machines able both to cut keys of one type, and to cut keys of the other type.
In addition, in known code-duplicating machines for MEDECO.TM. keys, the cutting involves a series of difficult, slow and non-instinctive operations, which are therefore subject to error.
Again in these known machines the key to be cut is generally positioned with that edge to be cut facing upwards with the cutter descending vertically onto it, to hence create a notch the cut of which is not perfectly rectilinear but instead is curved in accordance with the radius of the cutter. The result is that the engagement between the notch and relative pin is not perfect.
Finally, known duplicating machines for MEDECO.TM. keys have all their members accessible from the outside and hence subject to inevitable errors due to the presence and accumulation of swarf originating during cutting.